Utility meters, such as electricity meters, track the usage of utility commodities, for example, electricity. In the past, utility personnel physically observed meter data on mechanical counters or electronic displays. Because meters are typically located at the facility of the utility customer, such methods of meter reading are labor intensive and expensive.
Various types of remote meter reporting systems have been proposed and/or implemented. In one proposal, a wireless radio is employed. Wireless radio technology provides the advantage of not requiring a separate land-based communication line connection to the meter.
One problem with wireless radio communications in utility meters arises from the high power requirements of such radios. For example, wireless paging technology can require in excess of one amp of current at approximately eight to ten volts. This power requirement far exceeds the power requirement for the remainder of the meter circuitry. Typically, even more advanced polyphase electric utility meters only require substantially less than one amp of current. As a consequence, if the power supply in a utility meter is designed to accommodate wireless pager transmitters, the power supply must be drastically different, and generally much larger, then the power supply in the same utility meter without the transmitter.
The larger capacity power supply both occupies additional space within the meter and has increased cost. Because utility meter is only required to perform RF transmissions a very small fraction of the overall operating time of the meter, such additional power generating capacity goes unused for a substantial majority of the time. As a consequence, the relatively infrequent need for additional power does not necessarily justify the additional size, weight and cost issues that arise from the use of a large capacity power supply.
To address this issue, it is possible to employ a temporary or supplemental power source in the meter. For example, one or more batteries may be used to supplement the power supply output during transmission operations by the remote transmitter. In such a case, the power supply may be of a design suitable for the remaining meter circuitry. When extra power is needed for transmission, the extra power is provided by the batteries.
The reliance on batteries however, has drawbacks. As an initial matter, batteries used as supplemental power sources must necessarily be rechargeable batteries to be of any practical use. Indeed, the use of non-rechargeable batteries requiring frequent replacement would defeat the very purpose of implementing radio frequency transmission—to reduce the need for service visits to the meter. With regard to rechargeable batteries, nickel-metal hydride and lithium-ion batteries have been used in many applications, for example, in portable telephones and computers. However, such batteries are not particularly well-suited to the particular needs of a utility meter. For example, such batteries require relatively complex charging circuits, which would tend to negate the cost-savings of using the temporary power source. Moreover, all rechargeable batteries have a limited temperature range. Some rechargeable batteries lose their ability to hold a charge if exposed to out of range temperatures for an extended period.
Accordingly, a need exists for a method of providing supplemental, temporary power to a transmitter and possibly other circuits in a utility meter that overcomes the drawbacks associated with the use of rechargeable batteries.